In conventional practice, thin-film rare-earth permanent magnets are primarily obtained by the layering of materials based on Nd Fe B by vacuum vapor deposition or sputtering. The crystal structures of the layered formations obtained by these methods are disadvantageous in that the axis of easy magnetization is random, isotropic permanent magnet characteristics alone can be obtained in terms of magnetic characteristics, and only magnetic characteristics that are vastly inferior to those of anisotropic sintered permanent magnets can be obtained.
A method in which transition metal layers and magnet layers based on Nd Fe B are repeatedly layered in a specific thickness is described in Japanese Patent Application Laid-open No. H6-151226 as a means of improving magnetic characteristics. This method is disadvantageous in that the c axis, which is the axis of easy magnetization in Nd Fe B, is very difficult to completely align in the layering direction because the growth direction varies with the crystal direction of the underlying transition metal layers.
Another proposal concerns a vertically magnetized film in which a total of at least two layers is obtained by the alternate layering of at least one rare-earth metal film selected from Gd, Tb, and Dy, and of at least one transition metal film selected from Fe, Co, Ni, Cr, and Cu (Japanese Patent Application Laid-open No. S61 108112).
The magnetic characteristics are improved by layering transition metal films and rare-earth metal films on a vertically magnetized film in the order indicated. However, the use of a vertically magnetized film as the magnetic medium is presupposed, thus resulting in a very weak coercive force (about 1 kOe) and making it impossible to use the product as a permanent magnet.
In conventional practice, various proposals have been made concerning techniques for manufacturing thin-film permanent magnets by sputtering, vapor deposition, ion plating, and other techniques, but the magnets produced by all these methods had vastly inferior magnetic characteristics in comparison with anisotropic sintered permanent magnets.